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Philips Astonish TFInTroduCTIonThe Philips Astonish TF technology offers the advantages of time-of-flight (ToF) imaging, rapid list-modeToF reconstruction, point-spread function correction, and 4d respiratory-gated PET images.PET And PET/CT ToF TEChnologyPositron emission tomography (PeT) has become well TOF technology has addressed one of the importantestablished as an essential tool in molecular imaging, limitations of conventional PeT imaging. The imageallowing the visualization of metabolically active cells and reconstruction algorithm of conventional imaging assumesbiological processes.1,2 a uniform probability of an annihilation event being The wide use of PeT in oncology has been a driver somewhere along the line of response. By measuringof technological improvements in detector design and the difference between the arrival times of the individualarchitecture as well as in software applications, which photons of a generated photon pair, TOF technology allowshave combined to substantially improve image quality.3 the position of the annihilation event to be accurately locatedThe first PeT scanners operated in 2D, limiting potential along the line of response.4system sensitivity by up to 80%. 3D PeT imaging allows the The advantage of 3D TOF PeT over conventional 3Ddetection of photon pairs along lines of response between PeT in lesion detection during whole-body oncological scansplanes, resulting in a significant increase in system sensitivityand image quality.4 The combination of PeT with computed tomography PosITron EmIssIon TomogrAPhy (PET)(CT) was a major advance allowing the integration of PeT makes use of the annihilation event that is a consequencehigh-quality anatomical imaging and functional molecular of the collision of a positron released from a tracer moleculeimaging. in oncology, PeT/CT has become an established with a nearby electron. in oncology, the tracer is usuallyimaging technique for staging and restaging, and for 18F-labeled 2-fluoro-D-glucose (FDG), which is taken up atmonitoring responses, offering significant improvements a higher rate by cancer cells than normal cells, but which isover PeT or CT alone in a wide range of malignancies.5 it subsequently only partly metabolized, leading to intracellularhas also proven valuable in radiation therapy planning for accumulation.3 As the tracer decays, releasing a positron, thetarget-volume delineation and the planning of treatment pair of photons resulting from the subsequent annihilationstrategies.6 event travel in approximately 180° opposite paths Philips Astonish TF operates in 3D data acquisition (the line of response) and are detected by the scanningmode and utilizes the recent innovations of TOF technology device. Conventional PeT was unable to localize theand 4D PeT to further improve image resolution and to annihilation event along the line of response. Time-of-flightreduce potential image degradation resulting from patient (TOF) PeT does not have this limitation, and so has improvedor organ movement. The clinical evidence supporting these image quality, leading to increased diagnostic confidence.innovations is discussed below. Clinical Perspectives on Philips Astonish TF | 3

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Philips Astonish TF CAsE sTudy 2 TOF PET/CT with a low-activity protocol to evaluate treatment response A 50-year-old male patient had previously been diagnosed with follicular lymphoma. For staging and baseline measurements, PeT/CT had been carried out using 320 MBq 18F-FDG with imaging 60 minutes after injection. The patient was prescribed 6 cycles of chemotherapy. After the second therapy cycle, an abdominal mass was still present, and the decision was made to perform an interim scan in order toFigure 2. Comparison of ungated (top) and respiratory-gated assess treatment response using a low-activity protocol. The(bottom) PET/CT images of small pulmonary lesions. interim scan was performed with 185 MBq 18F-FDG using a(Source: Moinuddin A, et al.10) 64-channel GeMini PeT/CT system and TOF reconstruction.18 A BFigure 3. Respiratory-gated multiphasic CT images showing tumormovement during breathing. A: coronal (left) and sagittal (right) views atmaximum inhalation. B: the same contours mapped to the maximum Interim PET/CT scan of patient with follicular lymphoma acquired using aexpiration phase reveal tumor movement. (Source: Klahr P, et al.11) half-dose protocol demonstrating positive response to ongoing chemotherapy. Findings: While there was residual metabolically active diseaseA statistically significant difference in the area under the in mesenteric nodes, tracer uptake elsewhere had resolved.localized receiver operating characteristic (AlrOC) curve The overall response to chemotherapy was seen to befor non-TOF PeT and TOF PeT was evident for many positive, justifying continuation of treatment.readers. in every case, the accuracy of reading TOF imageswas higher than that of reading non-TOF images. For imagingof larger individuals (BMi ≥ 26) and for both larger andsmaller individuals with low-uptake lesions, a longer scan time the factor of timing, 4D PeT is able to reduce motioncombined with TOF PeT was found to give the best results. artifacts and achieve further gains in image quality. PhilipsFor a given lesion type and organ site, TOF PeT was able to Astonish TF makes use of 4D TOF PeT/CT technologydemonstrate a similarly high performance, irrespective of the to reduce motion artifacts, producing well-matched PeTsize of the scanned individuals. and CT images that correspond to a specific point in the respiratory cycle of a patient.9 There are two approaches to4d ToF PET achieving this:Cardiac and respiratory motion during data acquisition are • Prospective gating: images are collected at a specifican important source of image degradation during both PeT segment of the respiratory cycle of the patientand CT. This potential problem can have a negative impact – benefits include exposure to a low CT radiation dose,not only on quantitative accuracy during diagnostic imaging, due to the single-phase acquisition, and fast clinicalbut also on the precision of target-volume delineation interpretation, due to the smaller data volumeduring oncological radiation therapy. imaging of small or – limitations include the acquisition and interpretationlow-uptake lesions is particularly vulnerable to blurring into of data in only one phase, and the inability to evaluatethe background due to respiratory motion.9 By including tumor motion. Clinical Perspectives on Philips Astonish TF | 5

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ImAgIng 2.0 And PET/CT ImAgIng wITh PhIlIPsAsTonIsh TFThe world of radiology is rapidly evolving. radiologists andnuclear medicine physicians are under constant pressure tostreamline workflows in order to increase productivity andminimize costs while at the same time improving patientsatisfaction. imaging 2.0 is a concept that integrates Philipsequipment and software, producing a seamless imagingenvironment allowing specialists easy access to a multitudeof imaging modalities and software applications, aiming tomaximize both effectiveness and efficiency. imaging 2.0aims to:• enhance clinical collaboration and integration by creating hybrid modalities and medical networking tools that position radiology and nuclear medicine at the center of diagnosis and care 1.6 SUVmax 3.5 SUVmax• increase patient focus by developing patient-adaptive systems to provide excellent patient comfort during Figure 4. Comparison of TOF PET/CT images of small pulmonary scanning procedures nodule acquired without (left) and with (right) respiratory gating.• improve economic value by providing reliable tools and (Source: Benard F, et al.12) flexible applications that increase uptime.PeT/CT imaging is an essential element of imaging 2.0,combining high-quality anatomical imaging with functionalmolecular imaging. The Philips Astonish TF technology offersthe advantages of time-of-flight (TOF) imaging, full-fidelitylist-mode TOF reconstruction in seconds, point-spreadfunction correction, and 4D respiratory-gated PeT images.Astonish TF gives up to 30% better contrast resolution,compared with non-TOF technology, and with up to 5times higher sensitivity than non-TOF scanners, radiologistsand nuclear medicine physicians may be able to reduceradiopharmaceutical dosing in some or all of their studies. • retrospective gating: images are collected for the whole breathing cycle and are retrospectively assigned to a phase of the cycle – benefits include the acquisition of data for the whole breathing cycle, which increases flexibility to choose different phases, and the possibility to review breathing Figure 5. Reduction of motion artifacts using ultrafast PET acquisition in cine mode and breath-hold techniques to image non-small-cell lung cancer lesion. – limitations include exposure to an increased radiation Left: whole-body CT (top) and whole-body PET/CT (bottom). Center: dose during CT, increased complexity of data 4D CT (top) and 4D PET/CT (bottom). Right: breath-hold CT (top) and breath-hold PET/CT (bottom). (Source: Czyborra-Brinkman J.13) interpretation, and long reconstruction times. The flexibility of Astonish TF to use either approach has the potential to maximize the benefits of both to match with minimal tumor movement, and facilitates planning to specific clinical applications. There is a growing body of clinical maximize the proportion of the target tumor receiving the evidence supporting the use of respiratory gating techniques prescribed radiation dose most of the time, while reducing in specific settings. radiation to surrounding healthy tissues. Increasing the accuracy of the standardized uptake value (SUV)10 Enhancing small-lesion detection12 in a study of 24 patients with pulmonary lesions (≥ 1 cm), in a series of 15 patients with small pulmonary nodules, TOF whole-body PeT/CT scans were compared with and without PeT/CT images were acquired for the lesion of interest with respiratory gating (Figure 2). The mean sUvmax was 2.9 and without retrospective respiratory gating (Figure 4). For before respiratory gating and 3.5 after – a 22.5% increase. small lesions located within the lung parenchyma, respiratory lesion size was not found to be significantly different gating resulted in significantly reduced blurring, and increases (1.3 cm before and after gating). in sUvmax of 23–123%. Improving radiation therapy planning11 Facilitating patient motion management13 respiratory-gated multiphasic CT data sets have been A group of 17 patients with non-small-cell lung cancer shown to enable visualization of tumor movement during underwent a PeT/CT scan while breathing freely, followed breathing (Figure 3). This allows the identification of patients by an ultrafast PeT/CT scan holding their breath with deep 6 | Clinical Perspectives on Philips Astonish TF